it sounds to me like you must have a type of labial cyst
, either a bartholin's or a skene's cyst. that could be determined in exam. sometimes it can develop into an abcess, which is filled with pus. these are usually one one events that resolve, but sometimes thy can recur like you describe. often they can be treated with warm water soaks several times a day, but occasionally that doesn't help. depending on the situation, they can be surgically treated when conservative therapy doesn't help. this is a minor procedure that your gynecologist should be able to do. try are either removed entirely or opened and "marsupialized" after which they shouldn't come back again. exactly hat procedure is right depends on each situation. try to see your doctor when the cyst is swollen and he/she should be able to help you. I hope this helps, please let me know if you have any more questions.